Bone plate systems provide fixed-angle fixation of a bone plate by means of assigned screws for osteosynthesis in the human or animal body. Numerous bone plate systems are known that generally include a bone plate with an arrangement of a plurality of through-holes and associated screws. In addition to so-called bone screws, that is, screws that are screwed into the bone during fixation, fastening screws may be provided that are themselves not screwed into the bone but rather are screwed into a thread formed in the bone plate. Such fastening screws are then used for instance for fixing the bone screws (see for instance documents EP 1 702 577 A2, WO 2006/014436 A1, and AT 406 446 B). A fastening screw for fixing a plurality of bone screws is also used in the system for cervical vertebra in document DE 698 35 968 T2.
Document WO 2005/041769 A1 discloses a bone plate that is provided with longitudinal holes.
Fixed-angle plate-screw connections to osteosynthesis plates have the advantage of better anchoring of the bone plate to the bone. This is particularly advantageous with bone fractures close to a joint, since in this manner it is possible to better capture and fix bone fragments that are close to a joint. The advantage of fixed-angle plate-screw connections is even more significant in osteoporotic bone fractures close to a joint, since non-fixed-angle bone screws are not able to fix an osteoporotic bone as well.
Fixed-angle plate-screw connections can be divided into monoaxial and polyaxial plate-screw connections.
Examples of monoaxial fixed-angle plate-screw connections are presented in documents DE 10 2005 044 841 B4 and DE 10 2005 043 285 B3. These systems are characterized in that they have screw heads with male threads that engage in corresponding female threads of plates. If a screw is screwed in during an operation, the positive fit between the male thread of the screw head and the female thread of the bone plate effects a fixed-angle plate-screw connection during the last rotations of the screwing-in process.
Furthermore, bone plate systems have been suggested in which bone screws are variable with respect to their swivel or angular position relative to the bone plate during use. Such a bone plate system is described for instance in document DE 10 2006 000 948 A1. Document WO 2007/025520 A1 discloses a bone plate having at least one screw for fixed-angle fixation. Another example of a polyaxial fixed-angle plate-screw connection is disclosed in DE 10 2005 042 766 B4. The embodiment of a female thread from six female thread columns makes it possible to screw in spherical head screws having a special male thread in the polyaxial direction and to fix them in a fixed-angle manner during the last rotations of the screwing-in process. Such plate-screw systems have become increasingly common in clinical practice due to clinical advantages of a polyaxial fixed-angle fixation option.
A disadvantage of known fixed-angle bone plate systems is the lack of an option for drawing bone fragments to the bone plate during the process of tightening, since, due to its thread on the screw head, the thread of the screw head locks up in the bone plate during the last rotation. However, near a joint it is often necessary to draw in fragments in order to attain better restoration of the original anatomy. Moreover, for weakened osteoporotic bones there is a lack of plate systems with options for fixing a plurality of screws to or in a bone plate at a fixed angle in a narrow space.